1. Technical Field
The present invention relates to integrated circuits in general, and in particular to a method for fabricating integrated circuit devices. Still more particularly, the present invention relates to an enhanced shallow trench isolation method for fabricating radiation-tolerant integrated circuit devices.
2. Description of the Prior Art
Within a semiconductor integrated circuit (IC) device, device isolation regions can typically be found between two adjacent active components to prevent carriers from traveling between the two adjacent active components. For example, device isolation regions are conventionally formed between two adjacent field effect transistors (FETs) to reduce charge leakage to and from the two FETs. Often, device isolation regions take the form of thick field oxide regions extending below the surface of a semiconductor substrate. The most common technique for forming a thick field oxide region is to use a local oxidation of silicon (LOCOS) processing technique that is well-known to those skilled in the art of semiconductor processing. Details related to the LOCOS processing techniques can be found in VLSI technology, S. M. Sze, McGraw-Hill, 1983, which is incorporated by reference herein.
However, bird's beak regions formed in the LOCOS growth of field oxide regions are undesirable because they are typically too thin to provide any impact in terms of device isolation. Bird's beak regions nevertheless consume substrate surface area, limiting the extent to which the field oxide region can be shrunk while still providing desirable levels of device isolation. To provide higher device densities, it is therefore desirable to utilize a better device isolation structure such as shallow trench isolation (STI). With STI technology, a sharply defined trench is formed in the semiconductor substrate by, for example, anisotropic etching. The trench is filled with oxide back to the surface of a semiconductor substrate to provide a device isolation region. Trench isolation regions formed by STI have the advantages of providing device isolation across their entire lateral extent and of providing a more planar structure.
The present disclosure provides an improved STI method for fabricating a shallow trench that yields a desirable level of radiation tolerance so that the resulting semiconductor IC device can be used in high-radiation environments. Radiation tolerance refers to the ability of a semiconductor IC device to withstand radiation without alteration of its electrical characteristics. A semiconductor IC device is said to be radiation tolerant if it can continue to function within specifications after exposure to a specified amount of radiation.